Orion
Bristol Orion on display at the Rolls-Royce Heritage Trust, Derby
Type	Turboprop
Manufacturer	Bristol Siddeley
First run	1956
Major applications	Bristol Britannia

The Bristol Orion aero engine is a two-shaft turboprop intended for use in later marks of the Bristol Britannia and the Canadair CL-44. Although the engine was built and underwent a development program, the BE.25 Orion project was cancelled in 1958 by the British Ministry of Supply in favour of the Rolls-Royce Tyne.^[1] In addition, interest in turboprop-powered aircraft was beginning to wane, because of the successful introduction of the Boeing 707 and Douglas DC-8 jetliners into airline service.^[2]

The Orion gas generator had been chosen by French aircraft designer Wibault to power a vectored thrust aircraft^[3] which ultimately became the Hawker Siddeley P.1127 but with a Bristol Siddeley Orpheus gas generator which had a compressor derived from the Orion low pressure compressor.^[1]

Design and development

A single-stage HP turbine drove a five-stage all-axial HP compressor, while a three-stage LP turbine drove both the seven-stage LP compressor and the propeller, via a reduction gearbox. Thus the Orion used a shared-load LP turbine (like the Rolls-Royce Tyne), whereas its predecessor, the Bristol Proteus, had a free-power turbine. The combustor used separate flame cans.

One novel feature of the Orion was a derate from a thermodynamic rating of 9,000 shp at sea level, to enable a constant 5,150 ehp power level to be maintained up to 15,000 ft altitude.

The Orion project was cancelled in January 1958, at a reported total cost of £4.75 million (equivalent to $118,061,042 in 2021).^[4]

Applications

• Bristol Britannia
• Canadair CL-44

Specifications (BOn.1 Orion)

Data from Flightglobal archive.^[5]

General characteristics

• Type: Twin-spool turboprop
• Length: 112.3 in (2,850 mm)
• Diameter: 41.8 in (1,060 mm)
• Dry weight: 3,240 lb (1,470 kg)

Components

• Compressor: 7-stage LP axial flow compressor ; 5-stage HP axial flow compressor
• Combustors: Cannular combustor with 10 flame tubes
• Turbine: Single-stage HP turbine, 3-stage LP turbine
• Fuel type: Kerosene / JP-1
• Oil system: 3 independent systems at 80 psi (550 kPa)

Performance

• Maximum power output: Take-off 5,150 shp (3,840 kW) (equivalent horsepower)
• Overall pressure ratio: 10:1
• Air mass flow: 82 lb/s (37 kg/s)
• Specific fuel consumption: 0.39 lb/hp/h (0.066 kg/kW/ks) (equivalent horsepower)
• Thrust-to-weight ratio: 1.63 hp/lb (2.68 kW/kg) (equivalent horsepower)